Sodium tellurite is an inorganic tellurium compound with formula Na₂TeO₃. It is a water-soluble white solid and a weak reducing agent. Sodium tellurite is an intermediate in the extraction of the element, tellurium; it is a product obtained from anode slimes and is a precursor to tellurium.

Preparation

The main source of tellurium is from copper anode slimes, which contain

precious metal Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lustre. ...

s as well as various tellurides. These slimes are roasted with

sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...

and oxygen to produce sodium tellurite. :Ag₂Te + Na₂CO₃ + O₂ → 2Ag + Na₂TeO₃ + CO₂ (400–500 °C) This is a reaction with silver telluride. The telluride is oxidized to tellurite and the silver(I) is reduced to silver.

Purification

The

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of a tellurite solution yields purified tellurium. :Anode: 4OH⁻ → 2H₂O + O₂ + 4e⁻ :Cathode: TeO₃²⁻ + 3H₂O + 4e⁻ → Te + 6OH⁻

Structure and properties

Tellurium has properties similar to sulfur and selenium. In the anhydrous form Na₂TeO₃ the tellurium atoms are 6 coordinate, three Te-O at 1.87 Å and three at 2.9 Å, with distorted octahedra sharing edges. In the pentahydrate, Na₂TeO₃.5H₂O there are discrete tellurite anions, TeO₃²⁻ which are pyramidal. The Te-O distance is 1.85 - 1.86 Å and the O-Te-O angle is close to 99.5°. The tellurite anion is a weak base. Sodium tellurite would be similar to sodium selenite and sodium sulfite. Sodium tellurite is both a weak oxidizing agent and a weak reducing agent.

Tellurite-related reactions

:H₂TeO₃ → H⁺ + HTeO₃⁻ pK 2.48 Telluric acid loses a proton at this pKa. :HTeO₃⁻ → H⁺ + TeO₃²⁻ pK 7.7 Hydrogen tellurite loses a proton at this pKa to become the tellurite ion. This would happen in the reaction of tellurous acid with sodium hydroxide to make sodium tellurite. :TeO₂ + 2OH⁻ → TeO₃²⁻ + H₂O This is the reaction of tellurium dioxide with a base to make a tellurite salt.

Applications

Sodium tellurite improves the corrosion resistance of electroplated nickel layers. Solutions of sodium tellurite are used for black or blue-black coatings on iron, steel, aluminum, and copper. In microbiology, sodium tellurite can be added to the growth medium to isolate bacteria with an inherent physiological resistance to its toxicity.Borsetti, Francesca; Toninello, Antonio; Zannoni, Davide (2003). "Tellurite uptake by cells of the facultative phototroph Rhodobacter capsulatus is a pH-dependent process." Federation of European Biochemical Societies. Volume 554, Issue 3, 20 November 2003, pp. 315–318. Elsevier B.V.

References

*Cameo Chemicals. Sodium Tellurite. Retrieved March 8, 2009. Website: http://cameochemical.noaa.gov/chemical/5185. * {{Sodium compounds Tellurites Sodium compounds